Halogenated aromatic compounds are of much industrial importance as intermediates for medicines, agricultural chemicals, etc. At present, these intermediates are required to have much higher purity than heretofore. Except for monohalogenated benzenes, aromatic compounds with two or more substituents each have different isomers. For separating the mixture of those isomers into individual isomers through ordinary industrial distillation, an ultra-precision distillation device is needed, since the difference in boiling points between the isomers is small. However, at present, it is still extremely difficult to obtain high-purity products of a single isomer on an industrial scale. In addition, some types of halogenated aromatic compounds could not be separated into individual isomers through distillation. Recently, for separating a mixture of isomers that have heretofore been difficult or impossible to separate into individual ones, methods using adsorption separation have been developed. For example, JP-A 57-91933 and 58-131923 disclose a method of separating a single isomer from a mixture of chlorotoluene isomers through adsorption. Japanese Patent Application No. 9-335225 discloses a method of separating a single isomer from a mixture of chloroethylbenzene isomers through adsorption. JP-A 52-62229, 53-105434, 58-131924, 58-150524, 62-175433 and 4-330025 disclose a method of separating a single isomer from a mixture of dichlorobenzene isomers. JP-A 59-199642, 60-42340, 5-70383, 58-137795 and 3-20232 disclose a method of separating a mixture of dichlorotoluene isomers. JP-B 4-46933 discloses a process comprising removing HCl and water, which are formed in isomerization of a halogenated benzene derivative, through distillation, followed by separating a specific single isomer from the mixture of the resulting isomers by the use of an adsorbing and separating zeolite.